Help... Can somebody tell me what i'm I doing wrong?

I loaded the navboot to my pc, then I load the navboot file with the gif extractor program, the highlight the the hex code to preview the old image =====BMW========

selected the image to exchange, ok if I click on the hex code again I can preview my new logo. here is the problem when I replace the navboot file it does not have the new logo or the old one.

Any ideas
Thanks

X3Fever